Transient conduction block and its sequential changes have been rarely reported in human vasculitic neuropathy We performed serial nerve conduction studies during initial stage of nerve infarction in a patient with Churg-Strauss syndrome, who had acute ulnar nerve palsy 2 days before admission. At second day after the ulnar nerve palsy, the motor conduction block was detected in the segment between 12.5cm and 15cm above the ulnar groove; the amplitude of the compound muscle action potentials (CMAP) obtained with stimulation at 12 5cm above the ulnar groove was 7.4mV and that at 15cm was 0. 6mV. At fifth day, the motor conduction block disappeared and the amplitude of the CMAP obtained with stimulation at the site just distal to that segment reduced to 0. 6mV. The amplitude of the compound nerve action potentials (CNAP) of the finger-wrist segment was normal at admission but became unevokable at eighth day. The CNAP of the mixed nerve of the wrist-toelbow segment also gradually decreased and became similar with the amplitude of the wrist-to-axilla segment at twelfth day. These findings suggest that transient conduction block may be present in the metal stage of vasculitic neuropathy and that CMAP become unevokable earlier than CNAP.